The AKTIVER project (Active Flow control in compressor components of future Aircraft Engines) focuses on the research and design of innovative concepts for flow control in aerodynamically highly loaded intakes and compressors of future aircraft engines. The main objective of the project is a potential reduction in the overall length of engines, with a simultaneous increase in efficiency and crosswind resilience.  In order to achieve this goal, an energization of the three-dimensional boundary layer in the corresponding components provided by air blow-out, whereby the required compressed air is made available by recirculation via a static pressure gradient within the component. The blown-out air mass flow is additionally controlled by an actuator, which ensures the use of the system over different mission sections in an optimal way.

The analysis of the two engine components is carried out in close cooperation between the chair of Turbomachinery and Flight Propulsion (LTF) which will carried the compressor stage analysis and the Chair of Aerodynamics and Fluid Mechanics (AER) in charge of the intake analysis. For the compressor stage, the technical aspect lies of the fact that the compressor performance is strongly dominated by flow separations of 2D as well as 3D nature, which occur on the blades specially the endwall regions of rotor and stator rows. This determines the efficiency of compressors, limits of stability and hence the overall engine performance. Therefore, the project is aligned to the main funding policy goal of environmentally friendly aviation within the framework of quiet and efficient engines since the planned efficiency increase in combination with the possibility of engine mass reduction will lead to fuel saving and reduction of pollutant emissions.

Project goals

• Develop a detailed numerical and analytical consideration of the potential of the usage of an active control system within the compressor components of the engine for efficiency and operability improvements. A particular emphasis is given in the usage of a suitable actuator as the Active Flow Control system.
• It is expected to achieve an improvement of the compressor performance by the usage of this technology, e.g. lower required number of rotor and stator blades, reduction of losses and improvement of the operating range, higher efficiency per stage and thus more stability

The research project was funded by the sixth civil aviation research program (LuFo VI-2) of the German Federal Ministry for Economics and Climate Protection (BMWK) which supports research and technology projects in civil aviation in Germany. Grant number: 20E2113A

Brief description

In addition to electric aircraft propulsion systems and the use of hydrogen as a fuel, alternative fuels can be used to rapidly reduce the climate impact of air traffic. The project, which is funded by Munich Aerospace e.V., aims to investigate the behavior of a small gas turbine in terms of performance, engine health, and emissions when using alternative fuels. The following questions will be examined in more detail:

• What is the fuel-specific influence on engine functionality?
• What changes in engine performance can be observed in steady-state and transient operation?
• How do various drop-in fuels, sustainable aviation fuels, or eFuels affect emissions?

With regard to engine emissions, both gas phase and particulate emissions are considered.

The tests are carried out on the department's own Allison 250 C20B helicopter engine. This shaft power engine is very compact and the individual components are easily accessible, which facilitates adjustments and operation. This makes it possible to easily integrate new measurement technology. With regard to the fuel system, it is possible to switch quickly between regular Jet A-1 fuel supply and alternative fuel supply.

Project objectives

• Demonstrating the effects of alternative fuels on stationary and transient engine operation
• Investigating and presenting the influence of alternative fuels on gaseous and, above all, particulate emissions
• Identifying an alternative fuel that is optimized in terms of maximum energy release and minimum pollutant emissions
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Project partners

University of the Federal Armed Forces Munich

Munich Aerospace e.V.

Project manager

Alexander Rabl, M.Sc.

Foreign object damage (FOD) occurs when foreign particles are sucked into aircraft engines during flight. This is a persistent and critical problem, as FOD is unavoidable and has associated consequences.

Extensive research has been conducted to understand, detect, and prevent FOD events. However, further research is needed to improve the robustness of blades against these occurrences through specific design criteria. In collaboration with MTU Aero Engines, this project aims to develop new design criteria that increase blade robustness while maintaining aerodynamic performance. To achieve this goal, multidisciplinary optimizations are being performed using the AutoOpti optimizer, which is well known for its application in turbomachinery engineering. The first step in the analysis is to identify damage to blades in operation and determine the areas most likely to be affected. These areas are examined as part of the optimization process. The image below provides an overview of the FODs detected along an operating blade using a white light scanner. Establishing guidelines for designing more robust blades is crucial, but restoring blade integrity after damage is equally important. The second part of this project investigates the effects of repair blends on blade aerodynamic performance and structural behavior. A multidisciplinary approach is used to identify optimal blend geometries that improve blade performance and durability after repair.

Project Goals

• Identification of the most vulnerable areas of engine blades and development of new design criteria to increase their robustness against foreign object damage (FOD).
• Investigation of the blend process as the most effective method for removing damaged areas and restoring the original blade geometry. Given the erosive nature of this repair technique, it is important to evaluate its limitations and analyze the optimal blend shapes to ensure the integrity and performance of the repaired blades.

Project Partner

MTU Aero Engines

Person in charge

Simona Rocchi

Brief description

More environmentally friendly flying is playing an increasingly important role in the public eye and is part of research worldwide. With the Flightpath 2050 targets, there is a concrete effort to reduce the environmental impact of aviation. In this context, the fuel cell is seen as a promising concept for the future.

As part of the doctoral thesis, the potential of a fuel cell hybrid drive for aviation was investigated. Various degrees of hybridization and flight missions were examined and evaluated in a multidisciplinary manner. The aim was to identify for which area of application and for which class of aircraft a fuel cell drive makes sense.

Project objectives

• Determination of the potential of a fuel cell (hybrid) drive for aviation
• Investigation of the mutual influences on the design of the fuel cell (hybrid) drive and the aircraft
• Identification of the optimum area of application for a fuel cell drive in aviation

Project partner: MTU Aero Engines

Researcher: Jonas Schroeter

Brief description

The development of an aircraft engine is a complex and interdisciplinary process. The need for faster and more precise predictions means that a large number of dependencies must already be taken into account in the preliminary design phase. With the help of simplified and generalized physical laws, a method can be developed that achieves the desired level of detail in the design of the preliminary design phase. The mechanical design is an important step in the process and provides an initial component design layout based on parametric studies. Further disciplines can complement the results with an assessment of structural strength, a component-based weight estimate and an initial assessment of the component's service life. The great advantage of these methods is their flexibility, making it easier to develop new concepts independently of the knowledge-based designs. This project focused on the axial compressors and their interdependencies. For each main component of the compressor (blades, vanes, discs, casing), this project developed methods to parameterize the topology and developed structural aspects such as stresses, mechanical and manufacturing limits, low and high cycle fatigue, creep, disc burst and casing containment.

Project goals

• Development of multidisciplinary mechanical design methods for axial compressors
• Investigation of the impact of mechanical preliminary design methods during the preliminary design phase

Project partner: MTU Aero Engines AG

Reseacher: Ioannis Zaimis

Brief description

In times of strongly fluctuating feed-in of renewable electricity into the electrical grid, the need for control energy available at short notice is growing, which is why the use of agile gas turbine plants is becoming increasingly important. In order to achieve a fast start-up of the plant, it must be kept at aerodynamic partial load, which correlates with a reduction in process temperatures, pressures and geometric adjustments (e.g. guide vane adjustment). The changed conditions compared to the Aerodynamic Design Point (ADP) lead to the development of so-called “real geometry effects” in the annular channel (gaps, steps, edges, blade misalignment). The qualitative and quantitative assessment of these phenomena and their influence on turbine performance is the subject of current research.

Project objective

• Identification of decisive aerodynamic disturbance mechanisms on the performance of a highly loaded axial compressor
• Sensitivity study and potential analysis of desensitizing measures for a more robust compressor design

Project partners: Federal Ministry of Economics and Climate Protection, Rolls-Royce Deutschland Ltd & Co KG

Author: Jannik Petermann

Brief description

In order to reduce the environmental impact and improve the overall efficiency of an aircraft engine, thermal efficiency must be increased. The geared turbofan concept investigated by SAFRAN Aircraft Engines as part of CS2 aims to develop an extremely high efficiency engine architecture and ground test demonstrator in which increasing the core engine pressure ratio improves the thermal efficiency of the engine. However, a further increase in the core engine pressure ratio inevitably leads to a reduction in the size and cross-section of the core engine, which poses new challenges for the HPC design, especially for the rear compressor stages. Since the clearances between the rotor tips and the stator seals are absolutely limited to avoid friction, a reduction in blade height leads to larger relative blade clearances, which result in increased secondary flow phenomena, including stronger vortices at the blade tips, leakage flows at the shroud and increased boundary layer growth in the endwall regions.

These adverse aerodynamic effects impair the operating behavior (stall margin) and the aerodynamic performance (efficiency). To overcome the detrimental effects of pronounced leakage flows at the rotor tip, casing treatments (CT) are usually carried out. While CTs are known to enhance the flow in the rotor tip region, they usually result in a radial realignment of the flow and weaken the downstream compressor flow at lower span heights. This phenomenon will be particularly pronounced in the compact rear stages of future HPCs with high pressure ratios and low blade heights, and significantly increases the risk of premature stalling of the compressor due to weaker flow in the lower span region. To address these aerodynamic challenges, General Electric Deutschland (GEDE) is researching innovative HPC technologies including an advanced 3D blade design for HPC rear stages as part of the CS2 Joint Undertaking.

Project objectives

• To develop compressor flow treatment technologies that enhance full span flow, improve stability in a multi-stage compressor environment and maximize the potential of CT technology.
• The provision of a compressor test rig enabling validation of the HPC backstage technologies developed by GEDE and TUM-LTF, including detailed quantification of HPC performance and operability under representative engine conditions.

• The development and application of advanced unsteady pressure and temperature measurements that enable time-accurate entropy estimation and thus provide a detailed understanding of the flow physics and aerodynamic loss mechanisms within the developed HPC backstage concept.

  Project partner: GE

  Project team: Christian Köhler, Christian Schäffer